Can anyone relate??

Okay, so I've been on birth control for about 4 or 5 months now, taking the pill everyday at the same time and never missing one. I always get a normal period every month that lasts about 6 days. Last month my boyfriend came inside me for the firs time and my period was alittle spotty and only lasted 4 days. Could this be a sign of pregnancy or am I stressing out too much? Need a little reassurance pls!